Vit D: Discussion
- see: abnormalities associated with vitamin D.
- primary function of vitamin D is to maintain skeletal calcium homeostasis;
- promotes gut absorption of calcium (and absorption of phosphorous);
- promotes bone absorption;
- important for maintaining adequate quantities of Ca & Phos for bone formation thru its effects on the kidney & gut;
- in addition, it may have a direct effect on bone formation;
- proper functioning of the vitamin D system is necessary for PTH to maintain plasma calcium effectively, although drops in plasma
Ca occur only with severe Vit D depletion;
- it appears that only minute amounts of Vit D are necessary for PTH to carry out its actions on the bone and kidney;
- provitamin D2 (ergocalciferol from certain plants and animal fat) and 7-dehydroxycholesterol (endogenous) to form cholecalciferol (vit D3);
- provitamin D3 (7-dehydroxycholesterol synthesized in liver & stored in skin);
- in the skin, the provitamin is converted to the active form of cholecalciferol thru the activity of ultraviolet irradiation;
- hepatic hydroxylation to 25-OH vit D3;
- renal hydroxylation to 1,25 di OH D3;
- in proximal renal tubule: conversion to 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D, or 25,26-dihydroxyvitamin D);
- 1,25-dihydroxyvitamin D:
- is the most active of these metabolites;
- this hydroxylation is controled (increased) by PTH
- 24,25-dihydroxyvitamin D is the least active metabolite;
- concentration of 25-hydroxyvitamin D should remain between 20 - 32 ng per milliliter to avoid problems;
- Review Article: Vitamin D Deficiency
- Vit D Deficiency:
- see: abnormalities associated with vitamin D.
- primary effect of lack of Vit D is decrease in miceralization of newly formed bone matrix (osteoid);
- rate of bone formation is decreased;
- net result is less total bone & marked change in quality of bone;
- disease processes characterized by defective mineralizaiton caused by any problem resulting in inadequate amounts of Vit D or
low plasma PO4;
- in osteomalacia defective mineralizaiton results in relative increase in amount of osteoid (unmineralized bone matrix) in bone;
- persons who do not receive adequate daily sunlight exposure, such as those confined to home or nursing facility, may be at special
risk for vitamin D deficiency;
- in skeletally immature individuals, mineralization in the growth plates is also affected;
- osteomalacia in this setting is called rickets;
- in rickets, impaired mineralization of cartilage in zone of calcification arrests enchondral ossification & prevents formation of
- osteoporosis (see osteoporosis)
- in healthy young adults recommended daily allowance for Vit D is 400 U/day;
- w/ osteoporosis, supplementation with calcium and at least 800 U daily of vitamin D is treatment of choice;
- among elderly patients with hip fractures, 10 to 20 percent have impaired bone mineralization because of vitamin D deficiency;
- reference: Early intervention for postmenopausal osteoporosis. Scheiber LB. J Musculoskel Med. 1999:276.
- Vitamin Sub Types:
- provitamin D2:
- (ergocalciferol from certain plants and animal fat) and 7-dehydroxycholesterol (endogenous) to form cholecalciferol (vit D3);
- activity of D2 is short acting and may drop off after 3 days.
- ref: Vitamin D2 is much less effective than vitamin D3 in humans.
- provitamin D3:
- (7-dehydroxycholesterol synthesized in liver & stored in skin);
- this is the form that humans synthesize from sunlight (and is at least 3 times more potent than provitamin D2)
- supplementation with D3 may last up to 3 weeks;
- can be made from sheep's wool and fish oil;
- dietary sources of vitamin D3:
- cod liver oil (3.5 oz): 8500 international units
- raw herring, 3.5 oz: 900 international units
- salmon, 3.5 oz: 600 international units
- multivitamin: 400 international units
- milk, 1 cup: 100 international units
- Why the optimal requirement for Vitamin D3 is probably much higher than what is officially recommended for adults.
- l,25-Vitamin D3:
- note that this form of vitamin D, is chiefly indicated for patients with renal failure who cannot synthesis vitamin D3 to more active 1,25 Vit D3 hormone;
- unlike the standard Vit D3 whose dose is measured in international units, the 1,25 form is measured in micrograms;
- Vit D Toxicity:
- high doses of vitamin D may be toxic;
- toxicity has occurred at levels as low as 2,000 to 5,000 IU / day;
- it is not recommended that anyone consume more than 600 to 800 IU/day without a doctor's recommendation.
- vitamin D3 may promote antimicrobial peptides, cathelicidins;
- Scientists Find Why 'Sunshine' Vitamin D Is Crucial
- The antibiotic vitamin: deficiency in vitamin D may predispose people to infection
- Vitamin D Deficiency Study Raises New Questions About Disease And Supplements
- Vitamin D: its role and uses in immunology
- Vitamin D deficiency in patients with osteoarthritis undergoing total hip replacement: a cause for concern?
- Human cathelicidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3.
- Vitamin D regulation of cathelicidin in the skin: toward a renaissance of vitamin D in dermatology?
- Vitamin D3 Provides Skin With Protection From Harmful Microbes
- Multiple health concerns surface as winter, vitamin D deficiences arrive
- Vitamin D, Miracle Drug: Is It Science, or Just Talk?
- WELL; Vitamin D, Miracle Drug: Is It Science, or Just Talk?
- Prevalence of Vitamin D Insufficiency in African American Children with Forearm Fractures: A Preliminary Study
Serum levels of vitamin D, sunlight exposure, and knee cartilage loss in older adults: the Tasmanian older adult cohort study.
Should older people in residential care receive vitamin D to prevent falls? Results of a randomized trial.
A higher dose of vitamin d reduces the risk of falls in nursing home residents: a randomized, multiple-dose study
Vitamin D Sufficiency Screening in Preoperative Pediatric Orthopaedic Patients
The Effects of Vitamin D Deficiency in Athletes
Vitamin D Profile in National Football League Players
Bioavailability of Vitamin D and Its Metabolites in Black and White Adults
Original Text by Clifford R. Wheeless, III, MD.
Last updated by Data Trace Staff on Friday, November 13, 2015 10:05 am